(1) Field of the Invention:
The present invention relates to a ceramic insert cast piston. More particularly, the invention relates to a piston for an internal combustion engine in which a piston head made of a ceramic material is insert cast into a metal.
(2) Description of the Prior Art:
Recently, there have been trials with respect to pistons for internal combustion engines, wherein a piston head and a metal piston body are separately formed. Particularly, a ceramic having a high thermal resistance and a low heat conductivity is used as the piston head, and the ceramic piston head is integrally engaged with a metal piston body, whereby the combustion efficiency is increased, the engine output is improved, the discharge amount of hydrocarbons and carbon monoxide is reduced, and fuel consumption is decreased.
There is an insert casting as one of the methods by which the ceramic piston head (hereinafter referred to briefly as "ceramic head") is engaged with the metal piston body. According to the insert casting method, after the ceramic head member is deposited into a mold, a molten metal is cast into the mold with the ceramic head member, thereby integrating the ceramic head and the metal piston body.
However, this method suffers from the drawbacks that the ceramic head is likely to be broken due to the thermal shock which occurs during casting, and the large difference in the heat expansion between the ceramic material and the metal piston body loosens the engagement therebetween, so that when the piston is under reciprocal movement at a high speed, a piston head slips out from the piston body or the local stress is imposed upon the ceramic head, wherein fracture begins to occur.
Further, it is necessary to design the ceramic head in a form of a complicated core in order to prevent the ceramic head from slipping out from the metal piston body.